Magnetic random access memory having perpendicular enhancement layer

ABSTRACT

The present invention is directed to an STT-MRAM device including a plurality of magnetic tunnel junction (MTJ) memory elements. Each of the memory elements comprises a magnetic free layer structure and a magnetic reference layer structure with an insulating tunnel junction layer interposed therebetween; and a magnetic fixed layer separated from the magnetic reference layer structure by an anti-ferromagnetic coupling layer. The magnetic reference layer structure includes a first magnetic reference layer formed adjacent to the insulating tunnel junction layer and a second magnetic reference layer separated from the first magnetic reference layer by a first non-magnetic perpendicular enhancement layer, the first and second magnetic reference layers have a first invariable magnetization direction substantially perpendicular to layer plane thereof, the magnetic fixed layer has a second invariable magnetization direction that is substantially perpendicular to layer plane thereof and is opposite to the first invariable magnetization direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of the commonly assignedapplication bearing Ser. No. 14/053,231 filed on Oct. 14, 2013 by Gan etal. and entitled “Magnetic Random Access Memory Having PerpendicularEnhancement Layer,” which is a continuation-in-part of the commonlyassigned application bearing Ser. No. 14/026,163 filed on Sep. 13, 2013by Gan et al. and entitled “Perpendicular STTMRAM Device with BalancedReference Layer,” which is a continuation-in-part of the commonlyassigned application bearing Ser. No. 13/029,054 filed on Feb. 16, 2011by Zhou et al. and entitled “Magnetic Random Access Memory With FieldCompensating Layer and Multi-Level Cell,” and a continuation-in-part ofthe commonly assigned application bearing Ser. No. 13/277,187 filed onOct. 19, 2011 by Yiming Huai et al., and entitled “Memory System HavingThermally Stable Perpendicular Magneto Tunnel Junction (MTJ) and AMethod of Manufacturing Same,” which claims priority to U.S. ProvisionalApplication No. 61/483,314 and is a continuation-in-part of the commonlyassigned application bearing Ser. No. 12/965,733 filed on Dec. 10, 2010by Zhou et al., and entitled “Enhanced Magnetic Stiffness and Method ofMaking Same.” The present application is related to the commonlyassigned copending application bearing Ser. No. 13/737,897 filed on Jan.9, 2013, the commonly assigned copending application bearing Ser. No.14/021,917 filed on Sep. 9, 2013, the commonly assigned copendingapplication bearing Ser. No. 13/099,321 filed on May 2, 2011, and thecommonly assigned copending application bearing Ser. No. 13/928,263.

BACKGROUND

The present invention relates to a magnetic random access memory (MRAM)device, and more particularly, to a spin transfer torque MRAM deviceincluding at least a perpendicular enhancement layer in its memoryelement.

Spin transfer torque magnetic random access memory (STT-MRAM) is a newclass of non-volatile memory, which can retain the stored informationwhen powered off. A STT-MRAM device normally comprises an array ofmemory cells, each of which includes at least a magnetic memory elementand a selection element coupled in series between appropriateelectrodes. Upon application of an appropriate voltage or current to themagnetic memory element, the electrical resistance of the magneticmemory element would change accordingly, thereby switching the storedlogic in the respective memory cell.

FIG. 1 shows a conventional memory element for a STT-MRAM devicecomprising a magnetic reference layer 50 and a magnetic free layer 52with an insulating tunnel junction layer 54 interposed therebetween,thereby collectively forming a magnetic tunneling junction (MTJ) 56. Themagnetic reference layer 50 and free layer 52 have magnetizationdirections 58 and 60, respectively, which are substantiallyperpendicular to the layer plane. Therefore, the MTJ 56 is aperpendicular type comprising the magnetic layers 50 and 52 withperpendicular anisotropy. Upon application of an appropriate currentthrough the perpendicular MTJ 56, the magnetization direction 60 of themagnetic free layer 52 can be switched between two directions: paralleland anti-parallel with respect to the magnetization direction 58 of themagnetic reference layer 50. The insulating tunnel junction layer 54 isnormally made of a dielectric material with a thickness ranging from afew to a few tens of angstroms. However, when the magnetizationdirections 60 and 58 of the magnetic free layer 52 and reference layer50 are substantially parallel, electrons polarized by the magneticreference layer 50 can tunnel through the insulating tunnel junctionlayer 54, thereby decreasing the electrical resistivity of theperpendicular MTJ 56. Conversely, the electrical resistivity of theperpendicular MTJ 56 is high when the magnetization directions 58 and 60of the magnetic reference layer 50 and free layer 52 are substantiallyanti-parallel. Accordingly, the stored logic in the magnetic memoryelement can be switched by changing the magnetization direction 60 ofthe magnetic free layer 52.

One of many advantages of STT-MRAM over other types of non-volatilememories is scalability. As the size of the perpendicular MTJ 56 isreduced, the current required to switch the magnetization direction 60of the magnetic free layer 52 is reduced accordingly, thereby reducingpower consumption. However, the thermal stability of the magnetic layers50 and 52, which is required for long term data retention, also degradeswith miniaturization of the perpendicular MTJ 56.

For the foregoing reasons, there is a need for a STT-MRAM device thathas a thermally stable perpendicular MTJ memory element and that can beinexpensively manufactured.

SUMMARY

The present invention is directed to a spin transfer torque (STT)magnetic random access memory (MRAM) device that satisfy this need. ASTT-MRAM device having features of the present invention including aplurality of magnetic tunnel junction (MTJ) memory elements. Each of thememory elements comprises a magnetic free layer structure and a magneticreference layer structure with an insulating tunnel junction layerinterposed therebetween; and a magnetic fixed layer separated from themagnetic reference layer structure by an anti-ferromagnetic couplinglayer. The magnetic reference layer structure includes a first magneticreference layer formed adjacent to the insulating tunnel junction layerand a second magnetic reference layer separated from the first magneticreference layer by a first non-magnetic perpendicular enhancement layer,the first and second magnetic reference layers have a first invariablemagnetization direction substantially perpendicular to layer planethereof, the magnetic fixed layer has a second invariable magnetizationdirection that is substantially perpendicular to layer plane thereof andis opposite to the first invariable magnetization direction. Themagnetic free layer structure may include a magnetic free layer formedadjacent to the insulating tunnel junction layer and a magnetic deadlayer separated from the magnetic free layer by a second non-magneticperpendicular enhancement layer. The magnetic free layer has a variablemagnetization direction substantially perpendicular to layer planethereof. The magnetic dead layer comprises at least one ferromagneticelement but has no net magnetic moment in the absence of an externalmagnetic field.

According to an aspect of the presentation as applied to a perpendicularMTJ memory element, the memory element includes a magnetic tunneljunction (MTJ) structure in between a non-magnetic seed layer and anon-magnetic cap layer. The MTJ structure comprises a magnetic freelayer structure and a magnetic reference layer structure with aninsulating tunnel junction layer interposed therebetween; and a magneticfixed layer separated from the magnetic reference layer structure by ananti-ferromagnetic coupling layer. The magnetic reference layerstructure includes a first magnetic reference layer formed adjacent tothe insulating tunnel junction layer and a second magnetic referencelayer separated from the first magnetic reference layer by anintermediate magnetic reference layer. The first, second, andintermediate magnetic reference layers have a first invariablemagnetization direction substantially perpendicular to layer planethereof. The magnetic fixed layer has a second invariable magnetizationdirection that is substantially perpendicular to layer plane thereof andis opposite to the invariable magnetization direction.

According to another aspect of the presentation as applied to aperpendicular MTJ memory element, the memory element includes a magnetictunnel junction (MTJ) structure in between a non-magnetic seed layer anda non-magnetic cap layer. The MTJ structure comprises a magnetic freelayer structure and a magnetic reference layer with an insulating tunneljunction layer interposed therebetween; and a magnetic compensationlayer separated from the magnetic free layer by a non-magnetic tuninglayer. The magnetic reference layer has a first invariable magnetizationdirection substantially perpendicular to layer plane thereof. Themagnetic compensation layer has a second invariable magnetizationdirection that is substantially perpendicular to layer plane thereof andis substantially opposite to the first invariable magnetizationdirection.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings where:

FIG. 1 is a schematic view of a conventional perpendicular magnetictunnel junction;

FIG. 2 is a schematic circuit diagram of a STT-MRAM device according toan embodiment of the present invention;

FIGS. 3A and 3B are schematic views of an embodiment of the presentinvention as applied to a perpendicular MTJ memory element;

FIGS. 4A and 4B are schematic views of another embodiment of the presentinvention as applied to a perpendicular MTJ memory element;

FIGS. 5A and 5B are schematic views of still another embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 6A and 6B are schematic views of yet another embodiment of thepresent invention as applied to a perpendicular MTJ memory element;

FIGS. 7A and 7B are schematic views of still yet another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 8A and 8B are schematic views of yet still another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 9A and 9B are schematic views of still yet another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 10A and 10B are schematic views of yet still another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 11A and 11B are schematic views of still yet another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 12A and 12B are schematic views of yet still another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 13A and 13B are schematic views of still yet another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 14A and 14B are schematic views of yet still another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 15A and 15B are schematic views of still yet another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 16A and 16B are schematic views of yet still another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 17A and 17B are schematic views of still yet another embodiment ofthe present invention as applied to a perpendicular MTJ memory element;

FIGS. 18A and 18B are schematic views of embodiments of the presentinvention as applied to the perpendicular enhancement layer;

FIGS. 19A and 19B are schematic views of embodiments of the presentinvention as applied to the non-magnetic seed layer;

FIGS. 20A and 20B are schematic views of embodiments of the presentinvention as applied to the non-magnetic cap layer; and

FIGS. 21A and 21B are schematic views of embodiments of the presentinvention as applied to the non-magnetic tuning layer.

For purposes of clarity and brevity, like elements and components willbear the same designations and numbering throughout the Figures, whichare not necessarily drawn to scale.

DETALIED DESCRIPTION

In the Summary above and in the Detailed Description, and the claimsbelow, and in the accompanying drawings, reference is made to particularfeatures of the invention. It is to be understood that the disclosure ofthe invention in this specification includes all possible combinationsof such particular features. For example, where a particular feature isdisclosed in the context of a particular aspect or embodiment of theinvention, or a particular claim, that feature can also be used, to theextent possible, in combination with and/or in the context of otherparticular aspects and embodiments of the invention, and in theinvention generally.

Where reference is made herein to a material AB composed of element Aand element B, the material AB can be an alloy, a compound, or acombination thereof, except where the context excludes that possibility.

The term “noncrystalline” means an amorphous state or a state in whichfine crystals are dispersed in an amorphous matrix, not a single crystalor polycrystalline state. In case of state in which fine crystals aredispersed in an amorphous matrix, those in which a crystalline peak issubstantially not observed by, for example, X-ray diffraction can bedesignated as “noncrystalline.”

The term “magnetic dead layer” means a layer of supposedly ferromagneticmaterial that does not exhibit a net magnetic moment in the absence ofan external magnetic field. A magnetic dead layer of several atomiclayers may form in a magnetic film in contact with another layermaterial owing to intermixing of atoms at the interface. Alternatively,a magnetic dead layer may form as thickness of a magnetic film decreasesto a point that the magnetic film becomes superparamagnetic.

FIG. 2 is a schematic circuit diagram of a STT-MRAM device 100 accordingto an embodiment of the present invention. The STT-MRAM device 100comprises a plurality of memory cells 102, each of the memory cells 102including a selection transistor 104 coupled to a MTJ memory element106; a plurality of parallel word lines 108 with each being coupled to arespective row of the selection transistors 104 in a first direction;and a plurality of parallel bit lines 110 with each being coupled to arespective row of the memory elements 106 in a second directionperpendicular to the first direction; and optionally a plurality ofparallel source lines 112 with each being coupled to a respective row ofthe selection transistors 104 in the first or second direction.

The MTJ memory element 106 has a perpendicular MTJ structure thatincludes at least a perpendicular enhancement layer (PEL) to improve theperpendicular anisotropy of magnetic layers adjacent thereto. Anembodiment of the present invention as applied to a perpendicular MTJmemory element will now be described with reference to FIG. 3A.Referring now to FIG. 3A, the illustrated memory element 114 includes amagnetic tunnel junction (MTJ) structure 116 in between a non-magneticseed layer 118 and a non-magnetic cap layer 120. The MTJ structure 116comprises a magnetic free layer structure 122 and a magnetic referencelayer structure 124 with an insulating tunnel junction layer 126interposed therebetween. The magnetic reference layer structure 124 andthe magnetic free layer structure 122 are formed adjacent to thenon-magnetic seed layer 118 and cap layer 120, respectively. Themagnetic free layer structure 122 includes a first magnetic free layer128 formed adjacent to the insulating tunnel junction layer 126 and asecond magnetic free layer 130 separated from the first magnetic freelayer 128 by a first non-magnetic perpendicular enhancement layer (PEL)132. The magnetic reference layer structure 124 includes a firstmagnetic reference layer 134 formed adjacent to the insulating tunneljunction layer 126 and a second magnetic reference layer 136 separatedfrom the first magnetic reference layer 134 by a second non-magneticperpendicular enhancement layer 138. The first and the second magneticfree layers 128 and 130 have respectively a first and a second variablemagnetization directions 129 and 131 substantially perpendicular to thelayer plane thereof. The first and the second variable magnetizationdirections 129 and 131 may be parallel or anti-parallel to each other.The first and second magnetic reference layers 134 and 136 have a firstfixed magnetization direction 125 substantially perpendicular to thelayer plane thereof.

The stacking order of the individual layers in the MTJ structure 116 ofthe memory element 114 may be inverted without affecting the deviceperformance as illustrated in FIG. 3B. The memory element 114′ of FIG.3B has a MTJ structure 116′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 116. Accordingly,the magnetic free layer structure 122 and the magnetic reference layerstructure 124 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Another embodiment of the present invention as applied to a MTJ memoryelement is illustrated in FIG. 4A. The memory element 140 includes amagnetic tunnel junction (MTJ) structure 142 in between a non-magneticseed layer 118 and a non-magnetic cap layer 120. The MTJ structure 142comprises a magnetic free layer structure 122 and a magnetic referencelayer structure 144 with an insulating tunnel junction layer 126interposed therebetween. The magnetic reference layer structure 144 andthe magnetic free layer structure 122 are formed adjacent to thenon-magnetic seed layer 118 and cap layer 120, respectively. Themagnetic free layer structure 122 includes a first magnetic free layer128 formed adjacent to the insulating tunnel junction layer 126 and asecond magnetic free layer 130 separated from the first magnetic freelayer 128 by a non-magnetic perpendicular enhancement layer (PEL) 132.The first and the second magnetic free layers 128 and 130 haverespectively a first and a second variable magnetization directions 129and 131 substantially perpendicular to the layer plane thereof. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other. The magnetic reference layerstructure 144 has a fixed magnetization direction 145 substantiallyperpendicular to the layer plane thereof. The memory element 140 of FIG.4A is different from the memory element 114 of FIG. 3A in that themagnetic reference layer structure 144 is formed of a single magneticlayer.

The stacking order of the individual layers in the MTJ structure 142 ofthe memory element 140 may be inverted without affecting the deviceperformance as illustrated in FIG. 4B. The memory element 140′ of FIG.4B has a MTJ structure 142′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 142. Accordingly,the magnetic free layer structure 122 and the magnetic reference layerstructure 144 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Still another embodiment of the present invention as applied to a MTJmemory element is illustrated in FIG. 5A. The memory element 150includes a magnetic tunnel junction (MTJ) structure 152 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 152 comprises a magnetic free layer structure 154 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween. The magnetic reference layerstructure 124 and the magnetic free layer structure 154 are formedadjacent to the non-magnetic seed layer 118 and cap layer 120,respectively. The magnetic reference layer structure 124 includes afirst magnetic reference layer 134 formed adjacent to the insulatingtunnel junction layer 126 and a second magnetic reference layer 136separated from the first magnetic reference layer 134 by a non-magneticperpendicular enhancement layer 138. The magnetic free layer structure154 has a variable magnetization direction 155 substantiallyperpendicular to the layer plane thereof. The first and second magneticreference layers 134 and 136 have a first fixed magnetization direction125 substantially perpendicular to the layer plane thereof. The memoryelement 150 of FIG. 5A is different from the memory element 114 of FIG.3A in that the magnetic free layer structure 154 is formed of a singlemagnetic layer.

The stacking order of the individual layers in the MTJ structure 152 ofthe memory element 150 may be inverted without affecting the deviceperformance as illustrated in FIG. 5B. The memory element 150′ of FIG.5B has a MTJ structure 152′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 152. Accordingly,the magnetic free layer structure 154 and the magnetic reference layerstructure 124 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

The non-magnetic seed layer 118 of the memory elements 114, 114′, 140,140′, 150, and 150′ of FIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively,facilitates the optimal growth of the magnetic layer thereon to increaseperpendicular anisotropy. The non-magnetic seed layer 118 may alsoserves as a bottom electrode to the MTJ structures 116, 116′, 142, 142′,152, and 152′.

The non-magnetic cap layer 120 of the memory elements 114, 114′, 140,140′, 150, and 150′ of FIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively,functions as a top electrode to the MTJ structures 116, 116′, 142, 142′,152, and 152′, but may also improve the perpendicular anisotropy of themagnetic layer adjacent thereto during annealing.

For the MTJ structures 116, 116′, 142, 142′, 152, and 152′ of FIGS. 3A,3B, 4A, 4B, 5A, and 5B, at least one of the magnetic free layerstructure 122 and the magnetic reference layer structure 124 includes anon-magnetic perpendicular enhancement layer 132 or 138 therein. Theperpendicular enhancement layers 132 and 138 further improve theperpendicular anisotropy of the magnetic layers adjacent thereto duringdeposition and annealing.

Yet another embodiment of the present invention as applied to a MTJmemory element is illustrated in FIG. 6A. The memory element 160includes a magnetic tunnel junction (MTJ) structure 162 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 162 comprises a magnetic free layer structure 122 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, an anti-ferromagneticcoupling layer 164 formed adjacent to the magnetic reference layerstructure 124, and a magnetic fixed layer 166 formed adjacent to theanti-ferromagnetic coupling layer 164. The magnetic fixed layerstructure 166 and the magnetic free layer structure 122 are formedadjacent to the non-magnetic seed layer 118 and cap layer 120,respectively. The magnetic free layer structure 122 includes a firstmagnetic free layer 128 formed adjacent to the insulating tunneljunction layer 126 and a second magnetic free layer 130 separated fromthe first magnetic free layer 128 by a first non-magnetic perpendicularenhancement layer (PEL) 132. The magnetic reference layer structure 124includes a first magnetic reference layer 134 formed adjacent to theinsulating tunnel junction layer 126 and a second magnetic referencelayer 136 separated from the first magnetic reference layer 134 by asecond non-magnetic perpendicular enhancement layer 138. The first andthe second magnetic free layers 128 and 130 have respectively a firstand a second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer plane thereof. The first and the secondvariable magnetization directions 129 and 131 may be parallel oranti-parallel to each other. The first and second magnetic referencelayers 134 and 136 have a first fixed magnetization direction 125substantially perpendicular to the layer plane thereof. The magneticfixed layer 166 has a second fixed magnetization direction 167substantially opposite to the first fixed magnetization direction 125.The memory element 160 of FIG. 6A is different from the memory element114 of FIG. 3A in that the anti-ferromagnetic coupling layer 164 and themagnetic fixed layer 166 have been inserted in between the non-magneticseed layer 118 and the magnetic reference layer structure 124.

The stacking order of the individual layers in the MTJ structure 162 ofthe memory element 160 may be inverted without affecting the deviceperformance as illustrated in FIG. 6B. The memory element 160′ of FIG.6B has a MTJ structure 162′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 162. Accordingly,the magnetic free layer structure 122 and the magnetic fixed layerstructure 166 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Still yet another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 7A. The memory element 170includes a magnetic tunnel junction (MTJ) structure 172 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 172 comprises a magnetic free layer structure 122 and amagnetic reference layer structure 144 with an insulating tunneljunction layer 126 interposed therebetween, an anti-ferromagneticcoupling layer 164 formed adjacent to the magnetic reference layerstructure 144, and a magnetic fixed layer 166 formed adjacent to theanti-ferromagnetic coupling layer 164. The magnetic fixed layerstructure 166 and the magnetic free layer structure 122 are formedadjacent to the non-magnetic seed layer 118 and cap layer 120,respectively. The magnetic free layer structure 122 includes a firstmagnetic free layer 128 formed adjacent to the insulating tunneljunction layer 126 and a second magnetic free layer 130 separated fromthe first magnetic free layer 128 by a non-magnetic perpendicularenhancement layer (PEL) 132. The first and the second magnetic freelayers 128 and 130 have respectively a first and a second variablemagnetization directions 129 and 131 substantially perpendicular to thelayer plane thereof. The first and the second variable magnetizationdirections 129 and 131 may be parallel or anti-parallel to each other.The magnetic reference layer structure 144 has a first fixedmagnetization direction 145 substantially perpendicular to the layerplane thereof. The magnetic fixed layer 166 has a second fixedmagnetization direction 167 substantially opposite to the first fixedmagnetization direction 145. The memory element 170 of FIG. 7A isdifferent from the memory element 160 of FIG. 6A in that the magneticreference layer structure 144 is formed of a single magnetic layer.

The stacking order of the individual layers in the MTJ structure 172 ofthe memory element 170 may be inverted without affecting the deviceperformance as illustrated in FIG. 7B. The memory element 170′ of FIG.7B has a MTJ structure 172′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 172. Accordingly,the magnetic free layer structure 122 and the magnetic fixed layerstructure 166 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Yet still another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 8A. The memory element 180includes a magnetic tunnel junction (MTJ) structure 182 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 182 comprises a magnetic free layer structure 154 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, an anti-ferromagneticcoupling layer 164 formed adjacent to the magnetic reference layerstructure 124, and a magnetic fixed layer 166 formed adjacent to theanti-ferromagnetic coupling layer 164. The magnetic fixed layerstructure 166 and the magnetic free layer structure 122 are formedadjacent to the non-magnetic seed layer 118 and cap layer 120,respectively. The magnetic reference layer structure 124 includes afirst magnetic reference layer 134 formed adjacent to the insulatingtunnel junction layer 126 and a second magnetic reference layer 136separated from the first magnetic reference layer 134 by a non-magneticperpendicular enhancement layer 138. The magnetic free layer structure154 has a variable magnetization direction 155 substantiallyperpendicular to the layer plane thereof. The first and second magneticreference layers 134 and 136 have a first fixed magnetization direction125 substantially perpendicular to the layer plane thereof. The magneticfixed layer 166 has a second fixed magnetization direction 167substantially opposite to the first fixed magnetization direction 125.The memory element 180 of FIG. 8A is different from the memory element160 of FIG. 6A in that the magnetic free layer structure 154 is formedof a single magnetic layer.

The stacking order of the individual layers in the MTJ structure 182 ofthe memory element 180 may be inverted without affecting the deviceperformance as illustrated in FIG. 8B. The memory element 180′ of FIG.8B has a MTJ structure 182′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 182. Accordingly,the magnetic free layer structure 154 and the magnetic fixed layerstructure 166 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Comparing with the MTJ structures 116, 116′, 142, 142′, 152, and 152′ ofFIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively, the MTJ structures 162,162′, 172, 172′, 182, and 182′ of FIGS. 6A, 6B, 7A, 7B, 8A, and 8B,respectively, have the magnetic fixed layer 166 anti-ferromagneticallycoupled to the reference layers 124 and 144 through theanti-ferromagnetic coupling layer 164. The magnetic fixed layer 166 isnot an “active” layer like the magnetic reference layer structure andthe magnetic free layer structure, which along with the tunnel junctionlayer 126 collectively form a MTJ that changes resistivity when aspin-polarized current pass therethrough. The main function of themagnetic fixed layer 166, which has an opposite magnetization directioncompared with the magnetic reference layer structures 124 and 144, is tocancel, as much as possible, the external magnetic field exerted by themagnetic reference layer structures 124 and 144 on the magnetic freelayer structures 122 and 154, thereby minimizing the offset field or netexternal field in the magnetic free layer structures 122 and 154.

Still yet another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 9A. The memory element 190includes a magnetic tunnel junction (MTJ) structure 192 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 192 comprises a magnetic free layer structure 122 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, a non-magnetic tuning layer194 formed adjacent to the magnetic free layer structure 122, and amagnetic compensation layer 196 formed adjacent to the non-magnetictuning layer 194. The magnetic reference layer structure 124 and themagnetic compensation layer 196 are formed adjacent to the non-magneticseed layer 118 and cap layer 120, respectively. The magnetic free layerstructure 122 includes a first magnetic free layer 128 formed adjacentto the insulating tunnel junction layer 126 and a second magnetic freelayer 130 separated from the first magnetic free layer 128 by a firstnon-magnetic perpendicular enhancement layer (PEL) 132. The magneticreference layer structure 124 includes a first magnetic reference layer134 formed adjacent to the insulating tunnel junction layer 126 and asecond magnetic reference layer 136 separated from the first magneticreference layer 134 by a second non-magnetic perpendicular enhancementlayer 138. The first and the second magnetic free layers 128 and 130have respectively a first and a second variable magnetization directions129 and 131 substantially perpendicular to the layer plane thereof. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other. The first and secondmagnetic reference layers 134 and 136 have a first fixed magnetizationdirection 125 substantially perpendicular to the layer plane thereof.The magnetic compensation layer 196 has a second fixed magnetizationdirection 197 substantially opposite to the first fixed magnetizationdirection 125. The memory element 190 of FIG. 9A is different from thememory element 114 of FIG. 3A in that the non-magnetic tuning layer 194and the magnetic compensation layer 196 have been inserted in betweenthe magnetic free layer structure 122 and the non-magnetic cap layer120.

The stacking order of the individual layers in the MTJ structure 192 ofthe memory element 190 may be inverted without affecting the deviceperformance as illustrated in FIG. 9B. The memory element 190′ of FIG.9B has a MTJ structure 192′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 192. Accordingly,the magnetic compensation layer 196 and the magnetic reference layerstructure 124 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Yet still another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 10A. The memory element 200includes a magnetic tunnel junction (MTJ) structure 202 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 202 comprises a magnetic free layer structure 122 and amagnetic reference layer structure 144 with an insulating tunneljunction layer 126 interposed therebetween, a non-magnetic tuning layer194 formed adjacent to the magnetic free layer structure 122, and amagnetic compensation layer 196 formed adjacent to the non-magnetictuning layer 194. The magnetic reference layer structure 144 and themagnetic compensation layer 196 are formed adjacent to the non-magneticseed layer 118 and cap layer 120, respectively. The magnetic free layerstructure 122 includes a first magnetic free layer 128 formed adjacentto the insulating tunnel junction layer 126 and a second magnetic freelayer 130 separated from the first magnetic free layer 128 by anon-magnetic perpendicular enhancement layer (PEL) 132. The first andthe second magnetic free layers 128 and 130 have respectively a firstand a second variable magnetization directions 129 and 131 substantiallyperpendicular to the layer plane thereof. The first and the secondvariable magnetization directions 129 and 131 may be parallel oranti-parallel to each other. The magnetic reference layer structure 144has a first fixed magnetization direction 145 substantiallyperpendicular to the layer plane thereof. The magnetic compensationlayer 196 has a second fixed magnetization direction 197 substantiallyopposite to the first fixed magnetization direction 145. The memoryelement 200 of FIG. 10A is different from the memory element 190 of FIG.9A in that the magnetic reference layer structure 144 is formed of asingle magnetic layer.

The stacking order of the individual layers in the MTJ structure 202 ofthe memory element 200 may be inverted without affecting the deviceperformance as illustrated in FIG. 10B. The memory element 200′ of FIG.10B has a MTJ structure 202′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 202. Accordingly,the magnetic compensation layer 196 and the magnetic reference layerstructure 144 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Still yet another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 11A. The memory element 210includes a magnetic tunnel junction (MTJ) structure 212 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 212 comprises a magnetic free layer structure 154 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, a non-magnetic tuning layer194 formed adjacent to the magnetic free layer structure 122, and amagnetic compensation layer 196 formed adjacent to the non-magnetictuning layer 194. The magnetic reference layer structure 124 and themagnetic compensation layer 196 are formed adjacent to the non-magneticseed layer 118 and cap layer 120, respectively. The magnetic referencelayer structure 124 includes a first magnetic reference layer 134 formedadjacent to the insulating tunnel junction layer 126 and a secondmagnetic reference layer 136 separated from the first magnetic referencelayer 134 by a non-magnetic perpendicular enhancement layer 138. Themagnetic free layer structure 154 has a variable magnetization direction155 substantially perpendicular to the layer plane thereof. The firstand second magnetic reference layers 134 and 136 have a first fixedmagnetization direction 125 substantially perpendicular to the layerplane thereof. The magnetic compensation layer 196 has a second fixedmagnetization direction 197 substantially opposite to the first fixedmagnetization direction 125. The memory element 210 of FIG. 11A isdifferent from the memory element 190 of FIG. 9A in that the magneticfree layer structure 154 is formed of a single magnetic layer.

The stacking order of the individual layers in the MTJ structure 212 ofthe memory element 210 may be inverted without affecting the deviceperformance as illustrated in FIG. 11B. The memory element 210′ of FIG.11B has a MTJ structure 212′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 212. Accordingly,the magnetic compensation layer 196 and the magnetic reference layerstructure 124 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Yet still another embodiment of the present invention as applied to aperpendicular MTJ memory element is illustrated in FIG. 12A. The memoryelement 220 includes a magnetic tunnel junction (MTJ) structure 222 inbetween a non-magnetic seed layer 118 and a non-magnetic cap layer 120.The MTJ structure 220 comprises a magnetic free layer structure 122 anda magnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, a non-magnetic tuning layer194 formed adjacent to the magnetic free layer structure 122 oppositethe insulating tunnel junction layer 126, a magnetic compensation layer196 formed adjacent to the non-magnetic tuning layer 194 opposite themagnetic free layer structure 122, an anti-ferromagnetic coupling layer164 formed adjacent to the magnetic reference layer structure 124opposite the insulating tunnel junction layer 126, and a magnetic fixedlayer 166 formed adjacent to the anti-ferromagnetic coupling layer 164opposite the magnetic reference layer structure 124. The magnetic fixedlayer 166 and the magnetic compensation layer 196 are formed adjacent tothe non-magnetic seed layer 118 and cap layer 120, respectively. Themagnetic free layer structure 122 includes a first magnetic free layer128 formed adjacent to the insulating tunnel junction layer 126 and asecond magnetic free layer 130 separated from the first magnetic freelayer 128 by a first non-magnetic perpendicular enhancement layer (PEL)132. The magnetic reference layer structure 124 includes a firstmagnetic reference layer 134 formed adjacent to the insulating tunneljunction layer 126 and a second magnetic reference layer 136 separatedfrom the first magnetic reference layer 134 by a second non-magneticperpendicular enhancement layer 138. The first and the second magneticfree layers 128 and 130 have respectively a first and a second variablemagnetization directions 129 and 131 substantially perpendicular to thelayer plane thereof. The first and the second variable magnetizationdirections 129 and 131 may be parallel or anti-parallel to each other.The first and second magnetic reference layers 134 and 136 have a firstfixed magnetization direction 125 substantially perpendicular to thelayer plane thereof. The magnetic compensation layer 196 has a secondfixed magnetization direction 197 substantially opposite to the firstfixed magnetization direction 125. The magnetic fixed layer 166 has athird fixed magnetization direction 167 that is substantiallyperpendicular to the layer plane thereof and is substantially oppositeto the first fixed magnetization direction 125. The memory element 220of FIG. 12A is different from the memory element 190 of FIG. 9A in thatthe magnetic fixed layer 166 and the anti-ferromagnetic coupling layer164 have been inserted in between the magnetic reference layer structure124 and the non-magnetic seed layer 118.

The stacking order of the individual layers in the MTJ structure 222 ofthe memory element 220 may be inverted as illustrated in FIG. 12Bwithout affecting the device performance. The memory element 220′ ofFIG. 12B has a MTJ structure 222′ that has the same layers but with theinverted stacking order comparing with the MTJ structure 222.Accordingly, the magnetic compensation layer 196 and the magnetic fixedlayer 166 are formed adjacent to the non-magnetic seed layer 118 and caplayer 120, respectively.

Still yet another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 13A. The memory element 230includes a magnetic tunnel junction (MTJ) structure 232 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 232 comprises a magnetic free layer structure 234 and amagnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, an anti-ferromagneticcoupling layer 164 formed adjacent to the magnetic reference layerstructure 124, and a magnetic fixed layer 166 formed adjacent to theanti-ferromagnetic coupling layer 164. The magnetic fixed layerstructure 166 and the magnetic free layer structure 234 are formedadjacent to the non-magnetic seed layer 118 and cap layer 120,respectively. The magnetic free layer structure 234 includes a firstmagnetic free layer 128 formed adjacent to the insulating tunneljunction layer 126 and a magnetic dead layer 236 separated from thefirst magnetic free layer 128 by a first non-magnetic perpendicularenhancement layer (PEL) 132. The magnetic reference layer structure 124includes a first magnetic reference layer 134 formed adjacent to theinsulating tunnel junction layer 126 and a second magnetic referencelayer 136 separated from the first magnetic reference layer 134 by asecond non-magnetic perpendicular enhancement layer 138. The firstmagnetic free layer 128 has first a variable magnetization direction 129substantially perpendicular to the layer plane thereof. The first andsecond magnetic reference layers 134 and 136 have a first fixedmagnetization direction 125 substantially perpendicular to the layerplane thereof. The magnetic fixed layer 166 has a second fixedmagnetization direction 167 that is substantially perpendicular to thelayer plane thereof and is substantially opposite to the first fixedmagnetization direction 125. The memory element 230 of FIG. 13A isdifferent from the memory element 160 of FIG. 6A in that the secondmagnetic free layer 130 of the memory element 160 is replaced by themagnetic dead layer 236.

The stacking order of the individual layers in the MTJ structure 232 ofthe memory element 230 may be inverted as illustrated in FIG. 13Bwithout affecting the device performance. The memory element 230′ ofFIG. 13B has a MTJ structure 232′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 232. Accordingly,the magnetic free layer structure 234 and the magnetic fixed layerstructure 166 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Yet still another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 14A. The memory element 240includes a magnetic tunnel junction (MTJ) structure 242 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 242 comprises a magnetic free layer structure 234 and amagnetic reference layer structure 144 with an insulating tunneljunction layer 126 interposed therebetween, a non-magnetic tuning layer194 formed adjacent to the magnetic free layer structure 234, and amagnetic compensation layer 196 formed adjacent to the non-magnetictuning layer 194. The magnetic reference layer structure 144 and themagnetic compensation layer 196 are formed adjacent to the non-magneticseed layer 118 and cap layer 120, respectively. The magnetic free layerstructure 234 includes a first magnetic free layer 128 formed adjacentto the insulating tunnel junction layer 126 and a magnetic dead layer236 separated from the first magnetic free layer 128 by a non-magneticperpendicular enhancement layer (PEL) 132. The first magnetic free layer128 has a first variable magnetization direction 129 substantiallyperpendicular to the layer plane thereof. The magnetic reference layerstructure 144 has a first fixed magnetization direction 145substantially perpendicular to the layer plane thereof. The magneticcompensation layer 196 has a second fixed magnetization direction 197that is substantially perpendicular to the layer plane thereof and issubstantially opposite to the first fixed magnetization direction 145.The memory element 240 of FIG. 14A is different from the memory element200 of FIG. 10A in that the second magnetic free layer 130 of the memoryelement 200 is replaced by the magnetic dead layer 236.

The stacking order of the individual layers in the MTJ structure 242 ofthe memory element 240 may be inverted as illustrated in FIG. 14Bwithout affecting the device performance. The memory element 240′ ofFIG. 14B has a MTJ structure 242′ that has the same layers but with theinverted stacking order comparing to the MTJ structure 242. Accordingly,the magnetic compensation layer 196 and the magnetic reference layerstructure 144 are formed adjacent to the non-magnetic seed layer 118 andcap layer 120, respectively.

Still yet another embodiment of the present invention as applied to aperpendicular MTJ memory element is illustrated in FIG. 15A. The memoryelement 250 includes a magnetic tunnel junction (MTJ) structure 252 inbetween a non-magnetic seed layer 118 and a non-magnetic cap layer 120.The MTJ structure 250 comprises a magnetic free layer structure 234 anda magnetic reference layer structure 124 with an insulating tunneljunction layer 126 interposed therebetween, a non-magnetic tuning layer194 formed adjacent to the magnetic free layer structure 122 oppositethe insulating tunnel junction layer 126, a magnetic compensation layer196 formed adjacent to the non-magnetic tuning layer 194 opposite themagnetic free layer structure 122, an anti-ferromagnetic coupling layer164 formed adjacent to the magnetic reference layer structure 124opposite the insulating tunnel junction layer 126, and a magnetic fixedlayer 166 formed adjacent to the anti-ferromagnetic coupling layer 164opposite the magnetic reference layer structure 124. The magnetic fixedlayer 166 and the magnetic compensation layer 196 are formed adjacent tothe non-magnetic seed layer 118 and cap layer 120, respectively. Themagnetic free layer structure 234 includes a first magnetic free layer128 formed adjacent to the insulating tunnel junction layer 126 and amagnetic dead layer 236 separated from the first magnetic free layer 128by a first non-magnetic perpendicular enhancement layer (PEL) 132. Themagnetic reference layer structure 124 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by a second non-magneticperpendicular enhancement layer 138. The first magnetic free layer 128has a first variable magnetization direction 129 substantiallyperpendicular to the layer plane thereof. The first and second magneticreference layers 134 and 136 have a first fixed magnetization direction125 substantially perpendicular to the layer plane thereof. The magneticcompensation layer 196 has a second fixed magnetization direction 197substantially opposite to the first fixed magnetization direction 125.The magnetic fixed layer 166 has a third fixed magnetization direction167 that is substantially perpendicular to the layer plane thereof andis substantially opposite to the first fixed magnetization direction125. The memory element 250 of FIG. 15A is different from the memoryelement 220 of FIG. 12A in that the second magnetic free layer 130 ofthe memory element 220 is replaced by the magnetic dead layer 236.

The stacking order of the individual layers in the MTJ structure 252 ofthe memory element 250 may be inverted as illustrated in FIG. 15Bwithout affecting the device performance. The memory element 250′ ofFIG. 15B has a MTJ structure 252′ that has the same layers but with theinverted stacking order comparing with the MTJ structure 252.Accordingly, the magnetic compensation layer 196 and the magnetic fixedlayer 166 are formed adjacent to the non-magnetic seed layer 118 and caplayer 120, respectively.

Yet still another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 16A. The memory element 260includes a magnetic tunnel junction (MTJ) structure 262 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 262 comprises a magnetic free layer structure 122 and amagnetic reference layer structure 264 with an insulating tunneljunction layer 126 interposed therebetween, an anti-ferromagneticcoupling layer 164 formed adjacent to the magnetic reference layerstructure 264, and a magnetic fixed layer 166 formed adjacent to theanti-ferromagnetic coupling layer 164 opposite the magnetic referencelayer structure 264. The magnetic fixed layer structure 166 and themagnetic free layer structure 122 are formed adjacent to thenon-magnetic seed layer 118 and cap layer 120, respectively. Themagnetic free layer structure 122 includes a first magnetic free layer128 formed adjacent to the insulating tunnel junction layer 126 and asecond magnetic free layer 130 separated from the first magnetic freelayer 128 by a non-magnetic perpendicular enhancement layer (PEL) 132.The magnetic reference layer structure 264 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by an intermediate magnetic referencelayer 266. The first and the second magnetic free layers 128 and 130have respectively a first and a second variable magnetization directions129 and 131 substantially perpendicular to the layer plane thereof. Thefirst and the second variable magnetization directions 129 and 131 maybe parallel or anti-parallel to each other. The first, second, andintermediate magnetic reference layers 134, 136, and 266 have a firstfixed magnetization direction 125 substantially perpendicular to thelayer plane thereof. The magnetic fixed layer 166 has a second fixedmagnetization direction 167 substantially opposite to the first fixedmagnetization direction 125. The memory element 260 of FIG. 16A isdifferent from the memory element 160 of FIG. 6A in that theperpendicular enhancement layer 138 of the memory element 160 isreplaced by the intermediate magnetic reference layer 266.

The stacking order of the individual layers in the MTJ structure 262 ofthe memory element 260 may be inverted as illustrated in FIG. 16Bwithout affecting the device performance. The memory element 260′ ofFIG. 16B has a MTJ structure 262′ that has the same layers but with theinverted stacking order comparing with the MTJ structure 262.Accordingly, the magnetic free layer structure 122 and the magneticfixed layer structure 166 are formed adjacent to the non-magnetic seedlayer 118 and cap layer 120, respectively.

Still yet another embodiment of the present invention as applied to aMTJ memory element is illustrated in FIG. 17A. The memory element 270includes a magnetic tunnel junction (MTJ) structure 272 in between anon-magnetic seed layer 118 and a non-magnetic cap layer 120. The MTJstructure 272 comprises a magnetic free layer structure 234 and amagnetic reference layer structure 264 with an insulating tunneljunction layer 126 interposed therebetween, an anti-ferromagneticcoupling layer 164 formed adjacent to the magnetic reference layerstructure 264, and a magnetic fixed layer 166 formed adjacent to theanti-ferromagnetic coupling layer 164 opposite the magnetic referencelayer structure 264. The magnetic fixed layer structure 166 and themagnetic free layer structure 234 are formed adjacent to thenon-magnetic seed layer 118 and cap layer 120, respectively. Themagnetic free layer structure 234 includes a first magnetic free layer128 formed adjacent to the insulating tunnel junction layer 126 and amagnetic dead layer 236 separated from the first magnetic free layer 128by a non-magnetic perpendicular enhancement layer (PEL) 132. Themagnetic reference layer structure 264 includes a first magneticreference layer 134 formed adjacent to the insulating tunnel junctionlayer 126 and a second magnetic reference layer 136 separated from thefirst magnetic reference layer 134 by an intermediate magnetic referencelayer 266. The first magnetic free layers 128 has a first variablemagnetization direction 129 substantially perpendicular to the layerplane thereof. The first, second, and intermediate magnetic referencelayers 134, 136, and 266 have a first fixed magnetization direction 125substantially perpendicular to the layer plane thereof. The magneticfixed layer 166 has a second fixed magnetization direction 167substantially opposite to the first fixed magnetization direction 125.The memory element 270 of FIG. 17A is different from the memory element260 of FIG. 16A in that the second magnetic free layer 130 of the memoryelement 260 is replaced by the magnetic dead layer 236.

The stacking order of the individual layers in the MTJ structure 272 ofthe memory element 270 may be inverted as illustrated in FIG. 17Bwithout affecting the device performance. The memory element 270′ ofFIG. 17B has a MTJ structure 272′ that has the same layers but with theinverted stacking order comparing with the MTJ structure 272.Accordingly, the magnetic free layer structure 234 and the magneticfixed layer structure 166 are formed adjacent to the non-magnetic seedlayer 118 and cap layer 120, respectively.

Comparing with the MTJ structures 116, 116′, 142, 142′, 152, and 152′ ofFIGS. 3A, 3B, 4A, 4B, 5A, and 5B, respectively, the MTJ structures 192,192′, 202, 202′, 212, 212′, 222, 222′, 242, 242′, 252, and 252′ of FIGS.9A, 9B, 10A, 10B, 11A, 11B, 12A, 12B, 14A, 14B, 15A, and 15B,respectively, have the magnetic compensation layer 196 separated fromthe magnetic free layer structure 122, 154, or 234 by the non-magnetictuning layer 194. The magnetic compensation layer 196 is not an “active”layer like the magnetic reference layer structure and the magnetic freelayer structure, which along with the tunnel junction layer 126collectively form a MTJ that changes resistivity when a spin-polarizedcurrent pass therethrough. The main function of the magneticcompensation layer 196, which has an opposite magnetization directioncompared with the magnetic reference layer structures 124 and 144, is tocancel, as much as possible, the external magnetic field exerted by themagnetic reference layer structures 124 and 144 on the magnetic freelayer structures 122, 154 and 234, thereby minimizing the offset fieldor net external field in the magnetic free layer structures 122, 154,and 234.

For the MTJ memory elements 114, 114′, 140, 140′, 160, 160′, 170, 170′,190, 190′, 200, 200′, 222, 222′, 262, and 262′ of FIGS. 3A, 3B, 4A, 4B,6A, 6B, 7A, 7B, 9A, 9B, 10A, 10B, 12A, 12B, 16A, and 16B, respectively,where the magnetic free layer structure 122 comprises the first andsecond magnetic free layers 128 and 130, the first and second magneticfree layers 128 and 130 each may be formed of a magnetic materialcomprising cobalt (Co) and iron (Fe), such as but not limited tocobalt-iron (CoFe), cobalt-iron-boron (CoFeB),cobalt-iron-boron-titanium (CoFeBTi), cobalt-iron-boron-zirconium,(CoFeBZr), cobalt-iron-boron-hafnium (CoFeBHf),cobalt-iron-boron-vanadium (CoFeBV), cobalt-iron-boron-tantalum(CoFeBTa), cobalt-iron-boron-chromium (CoFeBCr), cobalt-iron-nickel(CoFeNi), cobalt-iron-titanium (CoFeTi), cobalt-iron-zirconium (CoFeZr),cobalt-iron-hafnium (CoFeHf), cobalt-iron-vanadium (CoFeV),cobalt-iron-niobium (CoFeNb), cobalt-iron-tantalum (CoFeTa),cobalt-iron-chromium (CoFeCr), cobalt-iron-molybdenum (CoFeMo),cobalt-iron-tungsten (CoFeW), cobalt-iron-aluminum (CoFeAl),cobalt-iron-silicon (CoFeSi), cobalt-iron-germanium (CoFeGe),cobalt-iron-phosphorous (CoFeP), or any combination thereof. For the MTJmemory elements 150, 150′, 180, 180′, 210, and 210′ of FIGS. 5A, 5B, 8A,8B, 11A, and 11B, respectively, where the magnetic free layer structure154 has a single magnetic layer, the magnetic free layer structure 154may comprise a magnetic material comprising Co and Fe, such as but notlimited to CoFe, CoFeB, CoFeBTi, CoFeBZr, CoFeBHf, CoFeBV, CoFeBTa,CoFeBCr, CoFeNi, CoFeTi, CoFeZr, CoFeHf, CoFeV, CoFeNb, CoFeTa, CoFeCr,CoFeMo, CoFeW, CoFeA1, CoFeSi, CoFeGe, CoFeP, or any combinationthereof. For the MTJ memory elements 232, 232′, 242, 242′, 252, 252′,272, and 272′ of FIGS. 13A, 13B, 14A, 14B, 15A, 15B, 17A, and 17B,respectively, in which the magnetic free layer structure 234 comprisesthe first magnetic free layer 128 and the magnetic dead layer 236. Thefirst magnetic free layer 128 may be formed of the same materials asdescribed above for the magnetic free layer structure 122. The magneticdead layer 236 may comprise one or more ferromagnetic elements, such asbut not limited to cobalt, iron, and nickel, and has no net magneticmoment in the absence of an external magnetic field. In one embodiment,the magnetic dead layer 236 has a nominal composition in which one ormore ferromagnetic elements collectively account for at least 30 atomicpercent.

For the MTJ memory elements 114, 114′, 150, 150′, 160, 160′, 180, 180′,190, 190′, 210, 210′, 220, 220′, 230, 230′, 250, and 250′ of FIGS. 3A,3B, 5A, 5B, 6A, 6B, 8A, 8B, 9A, 9B, 11A, 11B, 12A, 12B, 13A, 13B, 15A,and 15B, respectively, where the magnetic reference layer structure 124comprises the first and second magnetic reference layers 134 and 136,the first and second magnetic reference layers 134 and 136 each may beformed of a magnetic material comprising Co and Fe, such as but notlimited to CoFe, CoFeB, CoFeBTi, CoFeBZr, CoFeBHf, CoFeBV, CoFeBTa,CoFeBCr, CoFeNi, CoFeTi, CoFeZr, CoFeHf, CoFeV, CoFeNb, CoFeTa, CoFeCr,CoFeMo, CoFeW, CoFeA1, CoFeSi, CoFeGe, CoFeP, or any combinationthereof. The second magnetic reference layer 136 may alternatively bemade of cobalt, iron, or nickel. Moreover, the second magnetic referencelayer 136 may also have a magnetic superlattice structure comprisingrepeated alternating layers of two or more materials, such as but notlimited to (Co/Pt)_(n), (Co/Pd)_(n), (Co/Ni)_(n), (CoFe/Pt)_(n),(Co/Pt(Pd))_(n), or any combination thereof. Alternatively, the secondmagnetic reference layer 136 may be formed of a magnetic materialcomprising Co and Cr, such as but not limited to CoCr, CoCrB, CoCrPt,CoCrPtB, CoCrPd, CoCrTi, CoCrZr, CoCrHf, CoCrV, CoCrNb, CoCrTa, or anycombination thereof. For the MTJ memory elements 140, 140′, 170, 170′,200, 200′, 240, and 240′ of FIGS. 4A, 4B, 7A, 7B, 10A, 10B, 14A, and14B, respectively, where the magnetic reference layer structure 144comprises a magnetic layer, the magnetic reference layer structure 144may be formed of a magnetic material comprising Co and Fe, such as butnot limited to CoFe, CoFeB, CoFeBTi, CoFeBZr, CoFeBHf, CoFeBV, CoFeBTa,CoFeBCr, CoFeNi, CoFeTi, CoFeZr, CoFeHf, CoFeV, CoFeNb, CoFeTa, CoFeCr,CoFeMo, CoFeW, CoFeA1, CoFeSi, CoFeGe, CoFeP, or any combinationthereof. For the MTJ memory elements 260, 260′, 270, and 270′ of FIGS.16A, 16B, 17A, and 17B, respectively, in which the magnetic referencelayer structure 264 comprises the first and second magnetic referencelayers 134 and 136 with the intermediate magnetic reference layer 266interposed therebetween. The first and second magnetic reference layers134 and 136 each may be formed of the same materials as described abovefor the magnetic reference layer structure 124. The intermediatemagnetic reference layer 266 may be formed of a magnetic materialincluding tantalum as an alloying element, such as but not limited toCoFeBTa, CoFeNiBTa, FeTa, CoTa, FeBTa, CoBTa, NiTa, NiBTa, or anycombination thereof. Alternatively, the intermediate magnetic referencelayer 266 may be made of a material comprising Co and Fe, such as butnot limited to CoFe, CoFeB, CoFeBTi, CoFeBZr, CoFeBHf, CoFeBV, CoFeBTa,CoFeBCr, CoFeNi, CoFeTi, CoFeZr, CoFeHf, CoFeV, CoFeNb, CoFeTa, CoFeCr,CoFeMo, CoFeW, CoFeAl, CoFeSi, CoFeGe, CoFeP, or any combinationthereof.

In one embodiment, the first magnetic reference layer 134 of themagnetic reference structures 124 and 264 is made of a materialcomprising cobalt, iron, and boron, and has a thickness in the range ofabout 0.8 nm to about 1.2 nm. The second magnetic reference layer 136 ofthe magnetic reference structures 124 and 264 is made of a materialcomprising cobalt, iron, and boron, and has a thickness in the range ofabout 0.6 nm to about 1.5 nm.

For the perpendicular MTJ memory elements 160, 160′, 170, 170′, 180,180′, 220, 220′, 230, 230′, 250, 250′, 260, 260′, 270, and 270′ of FIGS.6A, 6B, 7A, 7B, 8A, 8B, 12A, 12B, 13A, 13B, 15A, 15B, 16A, 16B, 17A, and17B, respectively, the magnetic fixed layer 166 may be formed of amagnetic material comprising Co and Fe, such as but not limited to CoFe,CoFeB, CoFeBTi, CoFeBZr, CoFeBHf, CoFeBV, CoFeBTa, CoFeBCr, CoFeNi,CoFeTi, CoFeZr, CoFeHf, CoFeV, CoFeNb, CoFeTa, CoFeCr, CoFeMo, CoFeW,CoFeA1, CoFeSi, CoFeGe, CoFeP, or any combination thereof. Moreover, themagnetic fixed layer 166 may also have a magnetic superlattice structurecomprising repeated alternating layers of two or more materials, such asbut not limited to (Co/Pt)_(n), (Co/Pd)_(n), (Co/Ni)_(n), (CoFe/Pt)_(n),(Co/Pt(Pd))_(n), or any combination thereof. Alternatively, the magneticfixed layer 166 may be formed of a magnetic material comprising Co andCr, such as but not limited to CoCr, CoCrB, CoCrPt, CoCrPtB, CoCrPd,CoCrTi, CoCrZr, CoCrHf, CoCrV, CoCrNb, CoCrTa, or any combinationthereof. The anti-ferromagnetic coupling layer 164, which couples themagnetic fixed layer 166 to the magnetic reference layer structures 124and 144, may be made of ruthenium (Ru) or tantalum (Ta).

For the perpendicular MTJ memory elements 190, 190′, 200, 200′, 210,210′, 220, 220′, 240, 240′, 250, and 250′ of FIGS. 9A, 9B, 10A, 10B,11A, 11B, 12A, 12B, 14A, 14B, 15A, and 15B, respectively, the magneticcompensation layer 196 may be formed of a magnetic material comprisingCo and Fe, such as but not limited to CoFe, CoFeB, CoFeBTi, CoFeBZr,CoFeBHf, CoFeBV, CoFeBTa, CoFeBCr, CoFeNi, CoFeTi, CoFeZr, CoFeHf,CoFeV, CoFeNb, CoFeTa, CoFeCr, CoFeMo, CoFeW, CoFeA1, CoFeSi, CoFeGe,CoFeP, or any combination thereof. Moreover, the magnetic compensationlayer 196 may also have a magnetic superlattice structure comprisingrepeated alternating layers of two or more materials, such as but notlimited to (Co/Pt)_(n), (Co/Pd)_(n), (Co/Ni)_(n), (CoFe/Pt)_(n),(Co/Pt(Pd))_(n), or any combination thereof. Alternatively, the magneticcompensation layer 196 may be formed of a magnetic material comprisingCo and Cr, such as but not limited to CoCr, CoCrB, CoCrPt, CoCrPtB,CoCrPd, CoCrTi, CoCrZr, CoCrHf, CoCrV, CoCrNb, CoCrTa, or anycombination thereof.

The insulating tunnel junction layer 126 for all perpendicular MTJelements of FIGS. 3A-17A and 3B-17B may be formed of an insulatingmaterial, such as but not limited to magnesium oxide (MgO) or aluminumoxide (AlO_(x)).

The perpendicular enhancement layer (PEL) 132 in the magnetic free layerstructure 122 of FIGS. 3A, 3B, 4A, 4B, 6A, 6B, 7A, 7B, 9A, 9B, 10A, 10B,12A, 12B, 16A, and 16B, and in the magnetic free layer structure 234 ofFIGS. 13A, 13B, 14A, 14B, 15A, 15B, 17A, and 17B may be formed of anysuitable non-magnetic material. In an embodiment, the PEL 132 is formedof a PEL oxide, such as but not limited to magnesium oxide (MgO)titanium oxide (TiOx), zirconium oxide (ZrOx), hafnium oxide (HfOx),vanadium oxide (VOx), niobium oxide (NbOx), tantalum oxide (TaOx),chrome oxide (CrOx), molybdenum oxide (MoOx), tungsten oxide (WOx),rhodium oxide (RhOx), nickel oxide (NiOx), palladium oxide (PdOx),platinum oxide (PtOx), copper oxide (CuOx), silver oxide (AgOx),ruthenium oxide (RuOx), silicon oxide (SiOx), or any combinationthereof.

In another embodiment, the PEL 132 is formed of a PEL nitride, such asbut not limited to titanium nitride (TiNx), zirconium nitride (ZrNx),hafnium nitride (HfNx), vanadium nitride (VNx), niobium nitride (NbNx),tantalum nitride (TaNx), chrome nitride (CrNx), molybdenum nitride(MoNx), tungsten nitride (WNx), nickel nitride (NiNx), palladium nitride(PdNx), platinum oxide (PtOx), ruthenium nitride (RuNx), silicon nitride(SiNx), or any combination thereof.

In still another embodiment, the PEL 132 is formed of a PEL oxynitride,such as but not limited to titanium oxynitride (TiOxNy), zirconiumoxynitride (ZrOxNy), hafnium oxynitride (HfOxNy), vanadium oxynitride(VOxNy), niobium oxynitride (NbOxNy), tantalum oxynitride (TaOxNy),chrome oxynitride (CrOxNy), molybdenum oxynitride (MoOxNy), tungstenoxynitride (WOxNy), nickel oxynitride (NiOxNy), palladium oxynitride(PdOxNy), platinum oxyoxide (PtOxNy), ruthenium oxynitride (RuOxNy),silicon oxynitride (SiOxNy) or any combination thereof.

In yet another embodiment, the PEL 132 is formed of a PEL rutheniumoxide based material comprising ruthenium, oxygen, and at least oneother element, such as but not limited to TiRuOx, ZrRuOx, HfRuOx, VRuOx,NbRuOx, TaRuOx, CrRuOx, MoRuOx, WRuOx, RhRuOx, NiRuOx, PdRuOx, PtRuOx,CuRuOx, AgRuOx, or any combination thereof.

In still yet another embodiment, the PEL 132 is formed of a PEL metallicmaterial such as Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Rh, Pd, Pt, Cu, Ag,or any combination thereof. The PEL metallic material may also includenon-magnetic alloys comprising one or more magnetic elements and one ormore non-magnetic elements, such as but not limited to CoTi, CoZr, CoHf,CoV, CoNb, CoTa, CoFeTa, CoCr, CoMo, CoW, NiCr, NiTi, CoNiCr, CoNiTi, orany combination thereof. For these non-magnetic alloys containingmagnetic elements, the content of the magnetic elements is below thethreshold required for becoming magnetized. Alternatively, the PELmetallic material may also include nominally magnetic materials, such asCoFeB, that have extreme thin thickness, thereby rendering the nominallymagnetic materials non-magnetic. For example, CoFeB becomes non-magneticwhen the thickness thereof is less than about 0.7 nm.

The PEL 132 may include one or more sublayers therein. In an embodiment,the PEL 132 may include a first PEL sublayer 310 and a second PELsublayer 312 as illustrated in FIG. 18A. The first and second PELsublayers 310 and 312 each is formed of the above-described PEL oxide,PEL nitride, PEL oxynitride, PEL ruthenium oxide based material, or PELmetallic material. The first PEL sublayer 310 may form adjacent to thefirst magnetic free layer 128 or the second magnetic free layer 130. Inanother embodiment, the PEL 132 may include a first PEL sublayer 320, asecond PEL sublayer 322, and a third PEL sublayer 324 as illustrated inFIG. 18B. The first, second, and third PEL sublayers 320-324 each may beformed of the above-described PEL oxide, PEL nitride, PEL oxynitride,PEL ruthenium oxide based material, or PEL metallic material. The firstPEL sublayer 320 may form adjacent to the first magnetic free layer 128or the second magnetic free layer 130.

The perpendicular enhancement layer (PEL) 138 in the magnetic referencelayer structure 124 of FIGS. 3A, 3B, 5A, 5B, 6A, 6B, 8A, 8B, 9A, 9B,11A, 11B, 12A, 12B, 13A, 13B, 15A, and 15B may include one or moresublayers therein. In an embodiment, the PEL 138 is formed of theabove-described PEL oxide, PEL nitride, PEL oxynitride, PEL rutheniumoxide based material, or PEL metallic material. In another embodiment,the PEL layer 138 includes a first PEL sublayer 310 and a second PELsublayer 312 as illustrated in FIG. 18A. The first and second PELsublayers 310 and 312 each is formed of the above-described PEL oxide,PEL nitride, PEL oxynitride, PEL ruthenium oxide based material, or PELmetallic material. The first PEL sublayer 310 may form adjacent to thefirst magnetic reference layer 134 or the second magnetic referencelayer 136. In still another embodiment, the PEL layer 138 includes afirst PEL sublayer 320, a second PEL sublayer 322, and a third PELsublayer 324 as illustrated in FIG. 18B. The first, second, and thirdPEL sublayers 320-324 each is formed of the above-described PEL oxide,PEL nitride, PEL oxynitride, PEL ruthenium oxide based material, or PELmetallic material. The first PEL sublayer 320 may form adjacent to thefirst magnetic reference layer 134 or the second magnetic referencelayer 136.

The non-magnetic seed layer 118 of FIGS. 3-17A and 3-17B may include oneor more sublayers therein. In an embodiment, the non-magnetic seed layer118 is formed of the above-described PEL oxide, PEL nitride, PELoxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. In another embodiment, the non-magnetic seed layer 118includes a first seed sublayer 410 and a second seed sublayer 412 asillustrated in FIG. 19A. The first and second seed sublayers 410 and 412each is formed of the above-described PEL oxide, PEL nitride, PELoxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. The first seed sublayer 410 or the second seed sublayer 412may form adjacent to one of the magnetic layer structures 122, 124, 144,154, and 234 or one of the magnetic layers 166 and 196. In still anotherembodiment, the non-magnetic seed layer 118 includes a first seedsublayer 420, a second seed sublayer 422, and a third seed sublayer 424as illustrated in FIG. 19B. The first, second, and third seed sublayers420-424 each is formed of the above-described PEL oxide, PEL nitride,PEL oxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. The first seed sublayer 420 or the third seed sublayer 424 mayform adjacent to one of the magnetic layer structures 122, 124, 144,154, and 234 or one of the magnetic layers 166 and 196.

The non-magnetic cap layer 120 of FIGS. 3-17A and 3-17B may include oneor more sublayers therein. In an embodiment, the non-magnetic cap layer120 is formed of the above-described PEL oxide, PEL nitride, PELoxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. In another embodiment, the non-magnetic cap layer 120 includesa first cap sublayer 510 and a second cap sublayer 512 as illustrated inFIG. 20A. The first and second cap sublayers 510 and 512 each is formedof the above-described PEL oxide, PEL nitride, PEL oxynitride, PELruthenium oxide based material, or PEL metallic material. The first capsublayer 510 or the second cap sublayer 512 may form adjacent to one ofthe magnetic layer structures 122, 124, 144, 154, and 234 or one of themagnetic layers 166 and 196. In still another embodiment, thenon-magnetic cap layer 120 includes a first cap sublayer 520, a secondcap sublayer 522, and a third cap sublayer 524 as illustrated in FIG.20B. The first, second, and third cap sublayers 520-524 each may beformed of the above-described PEL oxide, PEL nitride, PEL oxynitride,PEL ruthenium oxide based material, or PEL metallic material. The firstcap sublayer 520 or the third cap sublayer 524 may form adjacent to oneof the magnetic layer structures 122, 124, 144, 154, and 234 or one ofthe magnetic layers 166 and 196.

The non-magnetic tuning layer 194 of FIGS. 9-17A and 9-17B may includeone or more sublayers therein. In an embodiment, the non-magnetic tuninglayer 194 is formed of the above-described PEL oxide, PEL nitride, PELoxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. In another embodiment, the non-magnetic tuning layer 194includes a first tuning sublayer 610 and a second tuning sublayer 612 asillustrated in FIG. 21A. The first and second tuning sublayers 610 and612 each is formed of the above-described PEL oxide, PEL nitride, PELoxynitride, PEL ruthenium oxide based material, or PEL metallicmaterial. The first tuning sublayer 610 or the second tuning sublayer612 may form adjacent to the magnetic compensation layer 196. In stillanother embodiment, the non-magnetic tuning layer 194 includes a firsttuning sublayer 620, a second tuning sublayer 622, and a third tuningsublayer 624 as illustrated in FIG. 21B. The first, second, and thirdtuning sublayers 620-624 each is formed of the above-described PELoxide, PEL nitride, PEL oxynitride, PEL ruthenium oxide based material,or PEL metallic material. The first tuning sublayer 620 or the thirdtuning sublayer 624 may form adjacent to the magnetic compensation layer196.

The previously described embodiments of the present invention have manyadvantages, including high perpendicular anisotropy and minimum offsetfield. It is important to note, however, that the invention does notrequire that all the advantageous features and all the advantages needto be incorporated into every embodiment of the present invention.

While the present invention has been shown and described with referenceto certain preferred embodiments, it is to be understood that thoseskilled in the art will no doubt devise certain alterations andmodifications thereto which nevertheless include the true spirit andscope of the present invention. Thus the scope of the invention shouldbe determined by the appended claims and their legal equivalents, ratherthan by examples given.

What is claimed is:
 1. A spin transfer torque magnetic random accessmemory (STT-MRAM) device comprising a plurality of memory elements, eachof said memory elements including a magnetic tunnel junction (MTJ)structure in between a non-magnetic seed layer and a non-magnetic caplayer, said MTJ structure comprising: a magnetic free layer structureand a magnetic reference layer structure with an insulating tunneljunction layer interposed therebetween; and a magnetic fixed layerseparated from said magnetic reference layer structure by ananti-ferromagnetic coupling layer, wherein said magnetic reference layerstructure includes a first magnetic reference layer formed adjacent tosaid insulating tunnel junction layer and a second magnetic referencelayer separated from said first magnetic reference layer by a firstnon-magnetic perpendicular enhancement layer, said first and secondmagnetic reference layers have a first invariable magnetizationdirection substantially perpendicular to layer plane thereof, saidmagnetic fixed layer has a second invariable magnetization directionthat is substantially perpendicular to layer plane thereof and isopposite to said first invariable magnetization direction.
 2. TheSTT-MRAM device according to claim 1, wherein said first non-magneticperpendicular enhancement layer is made of tantalum or tantalum nitride.3. The STT-MRAM device according to claim 1, wherein said secondmagnetic reference layer is made of cobalt, iron, or an alloy of cobaltand iron.
 4. The STT-MRAM device according to claim 1, wherein saidfirst magnetic reference layer is made of a material comprising cobalt,iron, and boron, and has a thickness in the range of about 0.8 nm toabout 1.2 nm, said second magnetic reference layer is made of a materialcomprising cobalt, iron, and boron, and has a thickness in the range ofabout 0.6 nm to about 1.5 nm.
 5. The STT-MRAM device according to claim1, wherein said magnetic free layer structure includes a first magneticfree layer formed adjacent to said insulating tunnel junction layer anda second magnetic free layer separated from said first magnetic freelayer by a second non-magnetic perpendicular enhancement layer, saidfirst and said second magnetic free layers have respectively a first anda second variable magnetization directions substantially perpendicularto layer plane thereof.
 6. The STT-MRAM device according to claim 5,wherein said second non-magnetic perpendicular enhancement layer is madeof magnesium oxide.
 7. The STT-MRAM device according to claim 5, whereineach of said first magnetic reference layer and said first magnetic freelayer is made of a material comprising cobalt, iron, and boron.
 8. TheSTT-MRAM device according to claim 1, wherein said magnetic free layerstructure includes a magnetic free layer formed adjacent to saidinsulating tunnel junction layer and a magnetic dead layer separatedfrom said magnetic free layer by a second non-magnetic perpendicularenhancement layer, said magnetic free layer has a variable magnetizationdirection substantially perpendicular to layer plane thereof, saidmagnetic dead layer comprises at least one ferromagnetic element but hasno net magnetic moment in absence of an external magnetic field.
 9. TheSTT-MRAM device according to claim 8, wherein said magnetic dead layeris made of a material comprising cobalt, iron, and boron, and has athickness less than about 0.7 nm.
 10. The STT-MRAM device according toclaim 8, wherein said second non-magnetic perpendicular enhancementlayer is made of magnesium oxide.
 11. The STT-MRAM device according toclaim 8, wherein each of said first magnetic reference layer and saidfirst magnetic free layer is made of a material comprising cobalt, iron,and boron.
 12. The STT-MRAM device according to claim 1, furthercomprising: a non-magnetic tuning layer formed adjacent to said magneticfree layer structure; and a magnetic compensation layer formed adjacentto said non-magnetic tuning layer opposite said magnetic free layerstructure, said magnetic compensation layer having said secondinvariable magnetization direction substantially opposite to said firstinvariable magnetization direction.
 13. The STT-MRAM device according toclaim 12, wherein said magnetic free layer structure includes a firstmagnetic free layer formed adjacent to said insulating tunnel junctionlayer and a second magnetic free layer separated from said firstmagnetic free layer by a second non-magnetic perpendicular enhancementlayer, said first and said second magnetic free layers have respectivelya first and a second variable magnetization directions substantiallyperpendicular to layer plane thereof.
 14. The STT-MRAM device accordingto claim 12, wherein said magnetic free layer structure includes amagnetic free layer formed adjacent to said insulating tunnel junctionlayer and a magnetic dead layer separated from said magnetic free layerby a second non-magnetic perpendicular enhancement layer, said magneticfree layer has a variable magnetization direction substantiallyperpendicular to layer plane thereof, said magnetic dead layer comprisesat least one ferromagnetic element but has no net magnetic moment inabsence of an external magnetic field.
 15. A spin transfer torquemagnetic random access memory (STT-MRAM) device comprising a pluralityof memory elements, each of said memory elements including a magnetictunnel junction (MTJ) structure in between a non-magnetic seed layer anda non-magnetic cap layer, said MTJ structure comprising: a magnetic freelayer structure and a magnetic reference layer structure with aninsulating tunnel junction layer interposed therebetween; and a magneticfixed layer separated from said magnetic reference layer structure by ananti-ferromagnetic coupling layer, wherein said magnetic reference layerstructure includes a first magnetic reference layer formed adjacent tosaid insulating tunnel junction layer and a second magnetic referencelayer separated from said first magnetic reference layer by anintermediate magnetic reference layer, said first, second, andintermediate magnetic reference layers have a first invariablemagnetization direction substantially perpendicular to layer planethereof, said magnetic fixed layer has a second invariable magnetizationdirection that is substantially perpendicular to layer plane thereof andis opposite to said first invariable magnetization direction.
 16. TheSTT-MRAM device according to claim 15, wherein said intermediatemagnetic reference layer is made of an alloy of iron and tantalum or analloy of cobalt, iron, boron, and tantalum.
 17. The STT-MRAM deviceaccording to claim 15, wherein said second magnetic reference layer ismade of cobalt, iron, or an alloy of cobalt and iron.
 18. The STT-MRAMdevice according to claim 15, wherein said first magnetic referencelayer is made of a material comprising cobalt, iron, and boron, and hasa thickness in the range of about 0.8 nm to about 1.2 nm, said secondmagnetic reference layer is made of a material comprising cobalt, iron,and boron, and has a thickness in the range of about 0.6 nm to about 1.5nm.
 19. The STT-MRAM device according to claim 15, wherein said magneticfree layer structure includes a first magnetic free layer formedadjacent to said insulating tunnel junction layer and a second magneticfree layer separated from said first magnetic free layer by a secondnon-magnetic perpendicular enhancement layer, said first and said secondmagnetic free layers have respectively a first and a second variablemagnetization directions substantially perpendicular to layer planethereof.
 20. The STT-MRAM device according to claim 19, wherein saidsecond non-magnetic perpendicular enhancement layer is made of magnesiumoxide.
 21. The STT-MRAM device according to claim 19, wherein each ofsaid first magnetic reference layer and said first magnetic free layeris made of a material comprising cobalt, iron, and boron.
 22. TheSTT-MRAM device according to claim 15, wherein said magnetic free layerstructure includes a magnetic free layer formed adjacent to saidinsulating tunnel junction layer and a magnetic dead layer separatedfrom said magnetic free layer by a second non-magnetic perpendicularenhancement layer, said magnetic free layer has a variable magnetizationdirection substantially perpendicular to layer plane thereof, saidmagnetic dead layer comprises at least one ferromagnetic element but hasno net magnetic moment in absence of an external magnetic field.
 23. TheSTT-MRAM device according to claim 22, wherein said magnetic dead layeris made of a material comprising cobalt, iron, and boron, and has athickness less than about 0.7 nm.
 24. The STT-MRAM device according toclaim 22, wherein said second non-magnetic perpendicular enhancementlayer is made of magnesium oxide.
 25. The STT-MRAM device according toclaim 22, wherein each of said first magnetic reference layer and saidfirst magnetic free layer is made of a material comprising cobalt, iron,and boron.
 26. A spin transfer torque magnetic random access memory(STT-MRAM) device comprising a plurality of memory elements, each ofsaid memory elements including a magnetic tunnel junction (MTJ)structure in between a non-magnetic seed layer and a non-magnetic caplayer, said MTJ structure comprising: a magnetic free layer structureand a magnetic reference layer with an insulating tunnel junction layerinterposed therebetween; and a magnetic compensation layer separatedfrom said magnetic free layer by a non-magnetic tuning layer, whereinsaid magnetic reference layer has a first invariable magnetizationdirection substantially perpendicular to layer plane thereof, saidmagnetic compensation layer has a second invariable magnetizationdirection that is substantially perpendicular to layer plane thereof andis substantially opposite to said first invariable magnetizationdirection.
 27. The STT-MRAM device according to claim 26, wherein saidnon-magnetic tuning layer is made of tantalum or tantalum nitride. 28.The STT-MRAM device according to claim 26, wherein said magnetic freelayer structure comprises a first magnetic free layer formed adjacent tosaid insulating tunnel junction layer and a second magnetic free layerseparated from said first magnetic free layer by a non-magneticperpendicular enhancement layer, said first and said second magneticfree layers have respectively a first and a second variablemagnetization directions substantially perpendicular to layer planethereof.
 29. The STT-MRAM device according to claim 28, wherein saidnon-magnetic perpendicular enhancement layer is made of magnesium oxide.30. The STT-MRAM device according to claim 26, wherein said magneticfree layer structure comprises a magnetic free layer formed adjacent tosaid insulating tunnel junction layer and a magnetic dead layerseparated from said magnetic free layer by a non-magnetic perpendicularenhancement layer, said magnetic free layer has a variable magnetizationdirection substantially perpendicular to layer plane thereof, saidmagnetic dead layer comprises at least one ferromagnetic element but hasno net magnetic moment in absence of an external magnetic field.
 31. TheSTT-MRAM device according to claim 30, wherein said non-magneticperpendicular enhancement layer is made of magnesium oxide.